I2C Synchronous Serial Two wire communications (plus ground) SCL – clock line SDA – bi-directional data line Message length: unrestricted Master – Slave Network Master Controls the information flow Source of SCL Slave Can synchronize data transfer by introducing wait states 9/12/2018 ECE 340 Lecture 24

I2C Synchronous Serial Multi-drop communications: Multiple transmitters and receivers on a common communications conductor Broadcast communications is possible One sender – many listeners Collision arbitration is required for multiple masters 9/12/2018 ECE 340 Lecture 24

I2C Definitions TERM DESCRIPTION Transmitter: The device which sends data to the bus Receiver: The device which receives data from the bus Master: The device which initiates a transfer, generates clock signals and terminates a transfer Slave: The device addressed by a master Multi-master: More than one master can attempt to control the bus at the same time without corrupting the message Arbitration: Procedure to ensure that, if more than one master simultaneously tries to control the bus, only one is allowed to do so and the winning message is not corrupted Synchronization: Procedure to synchronize the clock signals of two or more devices 9/12/2018 ECE 340 Lecture 24

I2C Physical Layer 9/12/2018 ECE 340 Lecture 24

I2C Framing 9/12/2018 ECE 340 Lecture 24

I2C Bit Transfer 9/12/2018 ECE 340 Lecture 24

I2C Byte Transfer Bit States Recessive (high == 1) Dominate (low == 0) 9/12/2018 ECE 340 Lecture 24

I2C Acknowledge 9/12/2018 ECE 340 Lecture 24

I2C Address 9/12/2018 ECE 340 Lecture 24

I2C Packet 9/12/2018 ECE 340 Lecture 24

Master Write Packet NACK – “Not ACKnowldege” can be used by slave to terminate packet 9/12/2018 ECE 340 Lecture 24

Master Read Packet Specification calls for Master to terminate with a NACK and a Stop bit 9/12/2018 ECE 340 Lecture 24

Master Write / Read Packet If changing direction of data transfer, then the master must resend the address in order to change the value of the R/W bit 9/12/2018 ECE 340 Lecture 24

“Mystery Code” int ReadIOXPort(unsigned char port) { #define IOX0 0x76 #define I2C_READ 0x01 // R/W bit char data_byte; int err; if(!port) // Assign I2C Address to Port Number port = IOX0; else port = IOX1; if (err=i2c_start_tx()) { // Start bit i2c_stop_tx(); return 0xff00 | err; } // Stretching error if (err=i2c_write_char(port + I2C_READ)) { // Send Address i2c_stop_tx(); return 0xfe00 | err; } // Stretching error If (err=i2c_read_char(&data_byte)) { // Read data i2c_stop_tx(); return 0xfc00 | err; } // Stretching error i2c_send_ack(); // Acknowledge data i2c_stop_tx(); // Stop bit return (unsigned int) data_byte; } // end ReadIOXPort “Mystery Code” 9/12/2018 ECE 340 Lecture 24

“Bit Banging” // Define these to change basic bit handling #define i2c_SCL_H() BitWrPortI(PDDDR,&PDDDRShadow,0,I2CSCLBit) #define i2c_SCL_L() BitWrPortI(PDDDR,&PDDDRShadow,1,I2CSCLBit) #define i2c_SDA_H() BitWrPortI(PDDDR,&PDDDRShadow,0,I2CSDABit) #define i2c_SDA_L() BitWrPortI(PDDDR,&PDDDRShadow,1,I2CSDABit) #define i2c_SCL() BitRdPortI(PDDR,I2CSCLBit) // read SCL #define i2c_SDA() BitRdPortI(PDDR,I2CSDABit) // read SDA 9/12/2018 ECE 340 Lecture 24

Clock Stretching int i2c_wSCL_H(){ // Tries to set SCL high & waits // Returns -1 if SCL stretch too long auto int delay_cnt; i2c_SCL_H(); cWAIT_5_us; // Set SCL HI delay_cnt = 0; while(i2c_SCL()==0 && delay_cnt < i2cClockStretchDelay) { cWAIT_5_us; delcnt++; } // end while if (i2c_SCL()==0) return -1; // Clock stretch too long return 0; } // end i2c_wSCL_H() 9/12/2018 ECE 340 Lecture 24

Start, Stop, & Ack int i2c_start_tx(){ // Try to send start pulse. // If clock stretch exceeded, return -1 else 0 if (i2c_wSCL_H()) return -1; // Try to set SCL HI i2c_SDA_H(); cWAIT_5_us; // Set SDA HI i2c_SDA_L(); cWAIT_5_us; // Set SDA LO i2c_SCL_L(); return 0; // Set SCL LO } // end i2c_start_tx void i2c_stop_tx() { i2c_SDA_L(); cWAIT_5_us; i2c_SCL_H(); cWAIT_5_us; i2c_SDA_H(); } // end i2c_stop_tx int i2c_send_ack() { i2c_SDA_L(); cWAIT_5_us; if (i2c_wSCL_H()) return -1; cWAIT_5_us; i2c_SCL_L(); cWAIT_5_us; i2c_SDA_H(); return 0; } // end i2c_send_ack 9/12/2018 ECE 340 Lecture 24

Write Char int i2c_write_char(char d){ // Writes char; returns -1 if no ACK from remote auto char i; for (i=0; I < 8; i++) { if (d & 0x80) i2c_SDA_H(); // send bit else i2c_SDA_L(); cWAIT_5_us; if (i2c_wSCL_H()) return -1; // Set SCL HI i2c_SCL_L(); cWAIT_5_us; // Set SCL LO d = d << 1; } // end for return i2c_check_ack(); } // end i2c_write_char() 9/12/2018 ECE 340 Lecture 24

Do you see any opportunities for improvement? Read char int i2c_read_char(char *ch) { auto char res,cnt; for ( cnt=0,res=0; cnt<8; cnt++ ) { i2c_SDA_H(); cWAIT_5_us; if (i2c_wSCL_H()) return -1; res <<= 1; if (i2c_SDA()) res |= 0x01; i2c_SCL_L(); cWAIT_5_us; } // end for *ch=res; return 0; } // end i2c_read_char Do you see any opportunities for improvement? 9/12/2018 ECE 340 Lecture 24

I2C on UI Project PCB 9/12/2018 ECE 340 Lecture 24

PCF8574 I2C Expander Can accommodate up to 8 devices on one I2C network 9/12/2018 ECE 340 Lecture 24

PCF8574 I2C Expander 9/12/2018 ECE 340 Lecture 24

Multi-Master I2C Network 9/12/2018 ECE 340 Lecture 24

I2C Arbitration 9/12/2018 ECE 340 Lecture 24

I2C Arbitration for 2 Masters 9/12/2018 ECE 340 Lecture 24

I2C References Specification: Tutorials http://www.semiconductors.philips.com/acrobat_download/literature/9398/39340011.pdf Tutorials Introduction to I2C (http://www.embedded.com/story/OEG20010718S0073) 9/12/2018 ECE 340 Lecture 24

Quiz List, and briefly describe, differences between RS232 and I2C communication in the Rabbit environment. Do see anything wrong with this? If (err=i2c_read_char(&data_byte)) { // Read data i2c_stop_tx(); return 0xfc00 | err; } // Stretching error 9/12/2018 ECE 340 Lecture 24